Blue-green algae. Coloured transmission electron micrograph of a single cell of the blue-green algae Microcystis aeruginosa (also known as Anacystis cyanea). Blue-green algae (cyanobacteria) are primitive algae; in structure they are related to bacteria. They are prokaryotes containing no membrane-bound nucleus; instead, as in bacteria, nuclear material is dispersed throughout the cell. Photosynthetic lamellae (thread-like structures, outer part of cell) are the primitive chloroplasts. M.aeruginosa cells are found in colonies; they bloom in late summer and may liberate a toxin that kills plankton, fish and birds. Magnification: x16,320 at 6x6cm size.